The innate immune system and the adaptive immune system work in concert in vertebrates to provide, among many other things, protection from pathogenic infection by micro-organisms. Anti-microbial vaccines may be formulated to engage both the innate and adaptive immune systems, but an effective response to vaccination is generally understood to involve a specific adaptive response to one or more of the immunogens present in a vaccine. In this way, multivalent vaccines, such as some pneumococcal vaccines, may be used to elicit a specific adaptive response to more than one serovar. Vaccines have also been described that confer some degree of cross-protective immunity, in which cross-reactivity to an antigen other than the immunogen confers a degree of protective immunity to heterologous microorganisms.